(1) Field of the Invention
The present invention relates to a variable valve system which is capable of modifying, for example, a valve lift (quantity) of an intake valve(s) or an exhaust valve(s) for an internal combustion engine and its driving mechanism.
(2) Description of Related Art
A Japanese Patent Application Publication No. 2005-273508 published on Oct. 6, 2005 exemplifies a previously proposed variable valve system for an internal combustion engine. The previously proposed variable valve system is applied to an intake valve side. A drive cam which is eccentric from an axial center of a drive axle is installed on an outer periphery of the drive axle revolving in synchronization with a rotation of a crankshaft. In addition, a rotating force of the drive cam is transmitted via a transmission mechanism in a multi-node link configuration and a swing cam is provided whose cam surface is slidably contacted on an upper surface of a valve lifter provided on an upper end of the intake valve to open to be operated against a biasing spring force of a valve spring.
Then, a driving mechanism including an electrically operated motor and ball screw means which is a speed-reduction mechanism varies a pivotal position of a control cam via a control axle in accordance with an engine driving state. Thus, a swing fulcrum of the transmission mechanism is varied so that a rollably contacted position of the cam surface of the swing cam against the upper surface of the valve lifter is varied. Thus, a valve lift (quantity) of the intake valve is variably controlled in accordance with the engine driving condition.